package org.apache.commons.net.ntp;                                                                                                                                                                                                                      
/*                                                                                                                                                                                                                                                       
 * Licensed to the Apache Software Foundation (ASF) under one or more                                                                                                                                                                                    
 * contributor license agreements.  See the NOTICE file distributed with                                                                                                                                                                                 
 * this work for additional information regarding copyright ownership.                                                                                                                                                                                   
 * The ASF licenses this file to You under the Apache License, Version 2.0                                                                                                                                                                               
 * (the "License"); you may not use this file except in compliance with                                                                                                                                                                                  
 * the License.  You may obtain a copy of the License at                                                                                                                                                                                                 
 *                                                                                                                                                                                                                                                       
 *      http://www.apache.org/licenses/LICENSE-2.0                                                                                                                                                                                                       
 *                                                                                                                                                                                                                                                       
 * Unless required by applicable law or agreed to in writing, software                                                                                                                                                                                   
 * distributed under the License is distributed on an "AS IS" BASIS,                                                                                                                                                                                     
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.                                                                                                                                                                              
 * See the License for the specific language governing permissions and                                                                                                                                                                                   
 * limitations under the License.                                                                                                                                                                                                                        
 */                                                                                                                                                                                                                                                      
                                                                                                                                                                                                                                                         
                                                                                                                                                                                                                                                         
import java.io.IOException;
import java.net.DatagramPacket;
import java.net.InetAddress;

import org.apache.commons.net.DatagramSocketClient;
                                                                                                                                                                                                                                                         
/***                                                                                                                                                                                                                                                     
 * The NTPUDPClient class is a UDP implementation of a client for the                                                                                                                                                                                    
 * Network Time Protocol (NTP) described in RFC 1305 as well as the                                                                                                                                                                                      
 * Simple Network Time Protocol (SNTP) in RFC-2030. To use the class,                                                                                                                                                                                    
 * merely open a local datagram socket with <a href="#open"> open </a>                                                                                                                                                                                   
 * and call <a href="#getTime"> getTime </a> to retrieve the time. Then call                                                                                                                                                                             
 * <a href="org.apache.commons.net.DatagramSocketClient.html#close"> close </a>                                                                                                                                                                          
 * to close the connection properly.                                                                                                                                                                                                                     
 * Successive calls to <a href="#getTime"> getTime </a> are permitted                                                                                                                                                                                    
 * without re-establishing a connection.  That is because UDP is a                                                                                                                                                                                       
 * connectionless protocol and the Network Time Protocol is stateless.                                                                                                                                                                                   
 *                                                                                                                                                                                                                                                       
 * @author Jason Mathews, MITRE Corp                                                                                                                                                                                                                     
 * @version $Revision: 489397 $ $Date: 2006-12-21 16:28:51 +0000 (Thu, 21 Dec 2006) $                                                                                                                                                                    
 ***/                                                                                                                                                                                                                                                    
                                                                                                                                                                                                                                                         
public final class NTPUDPClient extends DatagramSocketClient                                                                                                                                                                                             
{                                                                                                                                                                                                                                                        
    /*** The default NTP port.  It is set to 123 according to RFC 1305. ***/                                                                                                                                                                             
    public static final int DEFAULT_PORT = 123;                                                                                                                                                                                                          
                                                                                                                                                                                                                                                         
    private int _version = NtpV3Packet.VERSION_3;                                                                                                                                                                                                        
                                                                                                                                                                                                                                                         
    /***                                                                                                                                                                                                                                                 
     * Retrieves the time information from the specified server and port and                                                                                                                                                                             
     * returns it. The time is the number of miliiseconds since                                                                                                                                                                                          
     * 00:00 (midnight) 1 January 1900 UTC, as specified by RFC 1305.                                                                                                                                                                                    
     * This method reads the raw NTP packet and constructs a <i>TimeInfo</i>                                                                                                                                                                             
     * object that allows access to all the fields of the NTP message header.                                                                                                                                                                            
     * <p>                                                                                                                                                                                                                                               
     * @param host The address of the server.                                                                                                                                                                                                            
     * @param port The port of the service.                                                                                                                                                                                                              
     * @return The time value retrieved from the server.                                                                                                                                                                                                 
     * @exception IOException If an error occurs while retrieving the time.                                                                                                                                                                              
     ***/                                                                                                                                                                                                                                                
    public TimeInfo getTime(InetAddress host, int port) throws IOException                                                                                                                                                                               
    {                                                                                                                                                                                                                                                    
        // if not connected then open to next available UDP port                                                                                                                                                                                         
        if (!isOpen())                                                                                                                                                                                                                                   
        {                                                                                                                                                                                                                                                
            open();                                                                                                                                                                                                                                      
        }                                                                                                                                                                                                                                                
                                                                                                                                                                                                                                                         
        NtpV3Packet message = new NtpV3Impl();                                                                                                                                                                                                           
        message.setMode(NtpV3Packet.MODE_CLIENT);                                                                                                                                                                                                        
        message.setVersion(_version);                                                                                                                                                                                                                    
        DatagramPacket sendPacket = message.getDatagramPacket();                                                                                                                                                                                         
        sendPacket.setAddress(host);                                                                                                                                                                                                                     
        sendPacket.setPort(port);                                                                                                                                                                                                                        
                                                                                                                                                                                                                                                         
        NtpV3Packet recMessage = new NtpV3Impl();                                                                                                                                                                                                        
        DatagramPacket receivePacket = recMessage.getDatagramPacket();                                                                                                                                                                                   
                                                                                                                                                                                                                                                         
        /*                                                                                                                                                                                                                                               
         * Must minimize the time between getting the current time,                                                                                                                                                                                      
         * timestamping the packet, and sending it out which                                                                                                                                                                                             
         * introduces an error in the delay time.                                                                                                                                                                                                        
         * No extraneous logging and initializations here !!!                                                                                                                                                                                            
         */                                                                                                                                                                                                                                              
        TimeStamp now = TimeStamp.getCurrentTime();                                                                                                                                                                                                      
                                                                                                                                                                                                                                                         
        // Note that if you do not set the transmit time field then originating time                                                                                                                                                                     
        // in server response is all 0's which is "Thu Feb 07 01:28:16 EST 2036".                                                                                                                                                                        
        message.setTransmitTime(now);                                                                                                                                                                                                                    
                                                                                                                                                                                                                                                         
        _socket_.send(sendPacket);                                                                                                                                                                                                                       
        _socket_.receive(receivePacket);                                                                                                                                                                                                                 
                                                                                                                                                                                                                                                         
        long returnTime = System.currentTimeMillis();                                                                                                                                                                                                    
        // create TimeInfo message container but don't pre-compute the details yet                                                                                                                                                                       
        TimeInfo info = new TimeInfo(recMessage, returnTime, false);                                                                                                                                                                                     
                                                                                                                                                                                                                                                         
        return info;                                                                                                                                                                                                                                     
    }                                                                                                                                                                                                                                                    
                                                                                                                                                                                                                                                         
    /***                                                                                                                                                                                                                                                 
     * Retrieves the time information from the specified server on the                                                                                                                                                                                   
     * default NTP port and returns it. The time is the number of miliiseconds                                                                                                                                                                           
     * since 00:00 (midnight) 1 January 1900 UTC, as specified by RFC 1305.                                                                                                                                                                              
     * This method reads the raw NTP packet and constructs a <i>TimeInfo</i>                                                                                                                                                                             
     * object that allows access to all the fields of the NTP message header.                                                                                                                                                                            
     * <p>                                                                                                                                                                                                                                               
     * @param host The address of the server.                                                                                                                                                                                                            
     * @return The time value retrieved from the server.                                                                                                                                                                                                 
     * @exception IOException If an error occurs while retrieving the time.                                                                                                                                                                              
     ***/                                                                                                                                                                                                                                                
    public TimeInfo getTime(InetAddress host) throws IOException                                                                                                                                                                                         
    {                                                                                                                                                                                                                                                    
        return getTime(host, NtpV3Packet.NTP_PORT);                                                                                                                                                                                                      
    }                                                                                                                                                                                                                                                    
                                                                                                                                                                                                                                                         
    /***                                                                                                                                                                                                                                                 
     * Returns the NTP protocol version number that client sets on request packet                                                                                                                                                                        
     * that is sent to remote host (e.g. 3=NTP v3, 4=NTP v4, etc.)                                                                                                                                                                                       
     *                                                                                                                                                                                                                                                   
     * @return  the NTP protocol version number that client sets on request packet.                                                                                                                                                                      
     * @see #setVersion(int)                                                                                                                                                                                                                             
     ***/                                                                                                                                                                                                                                                
    public int getVersion()                                                                                                                                                                                                                              
    {                                                                                                                                                                                                                                                    
        return _version;                                                                                                                                                                                                                                 
    }                                                                                                                                                                                                                                                    
                                                                                                                                                                                                                                                         
    /***                                                                                                                                                                                                                                                 
     * Sets the NTP protocol version number that client sets on request packet                                                                                                                                                                           
     * communicate with remote host.                                                                                                                                                                                                                     
     *                                                                                                                                                                                                                                                   
     * @param version the NTP protocol version number                                                                                                                                                                                                    
     ***/                                                                                                                                                                                                                                                
    public void setVersion(int version)                                                                                                                                                                                                                  
    {                                                                                                                                                                                                                                                    
        _version = version;                                                                                                                                                                                                                              
    }                                                                                                                                                                                                                                                    
                                                                                                                                                                                                                                                         
}                                                                                                                                                                                                                                                        
